1. Field
This disclosure relates generally to power consumption reduction in a computer system, and more specifically but not exclusively, to methods and apparatus for caching memory content to facilitate instant-on resuming from a hibernation state for low power computing platforms.
2. Description
Ultra mobility is becoming a trend for today's personal computers (PCs). Users expect many PCs, especially laptop PCs, to have all-day battery life and quick responding capability. To extend battery life, a PC needs to be aggressively put into low power idle states, much more aggressively than most PCs currently are. Today most PCs use Advanced Configuration and Power Interface (ACPI) to manage their power consumption. The ACPI enables an operating system (OS) to control the amount of power consumed by a PC. With the ACPI, the OS can put a PC into the S4 (hibernate) state or the S3 (sleep) state when the PC is not active for a certain period of time. A PC consumes much more power under the S3 state than under the S4 states. Thus, to extend battery life and hence to become more mobile, it is desirable to put a PC into the S4 state over long periods of inactivity. However, while the S4 state is ideal for conserving power, it is a high-latency sleep state since the system context is saved to (and read back on resume from) the hard disk drive (HDD). Given that the hand-top PCs normally need to use micro-drives (to achieve the form-factor & cost targets), this results in resume times varying widely from 3-4 seconds (S3 resume) to 30 plus seconds (S4 resume using micro-drives). In other words, while the S4 state conserves more power than the S3 state, it slows down a PC's responding time during wakeup, which becomes less acceptable in today's fast-pace computing environment. Thus, it is desirable to reduce S4 resume time.